JPH0727865B2 - Hetero interface formation method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a hetero interface, and more particularly to a method for forming a high quality hetero interface of a compound semiconductor by a molecular beam epitaxy method.

[Prior Art] Most of compound semiconductor devices such as a two-dimensional electron gas transistor and a quantum well laser utilize a heterojunction in which different kinds of semiconductor crystals are joined. The properties of the heterojunction interface (hereinafter referred to as the heterointerface) affect carrier scattering, light emission, absorption, etc., and greatly affect device characteristics. Therefore, it is important to form a high-quality interface that is flat and steep and has no impurities or defects. Molecular beam epitaxy (hereinafter referred to as MBE) is a means of forming such a steep hetero interface.
The law is widely practiced.

Figure 2 shows the M commonly used to perform this MBE method.
FIG. 1 is a schematic cross-sectional view of a BE apparatus, in which a raw material containing an element that constitutes a desired crystal is heated in a growth chamber 1 kept in an ultrahigh vacuum by a vacuum pump 9 such as an ion pump to form a molecular beam. Molecular beam source 20,21,22,23 for ejecting each element to
This molecular beam source 20, 21, 22, 23 is provided with a substrate holder 3 for heating and holding the substrate 4 so that the temperature can be controlled independently of each other, and the molecular beam sources 20, 21, 22, 23 are directed toward the substrate 4. Epitaxial growth is performed by ejecting the molecular beam of the raw material element. MBE
In the method, shutters 5a-5d arranged in front of each molecular beam source are used.
It is possible to continue the individual molecular beam by opening and closing, and to control the modulation of the molecular beam intensity by setting the temperature of the evaporation source of each raw material.

Conventionally, as a method of forming a flat and steep hetero interface on the order of atoms in the MBE method, each molecular beam source 20 to 23
Growth is interrupted at the interface by closing the shutters 5a-5d of
A method of increasing the flatness of the interface by waiting for several tens of seconds to several minutes has been reported for the GaAs / AlGaAs hetero system (Japanese Journal of Applied.
Physics (Jpn.J.Appl.Phys.), 24, (1985), L417
page). This method is called the interface waiting MBE method here.

FIG. 3 is an explanatory view schematically explaining a conventional hetero interface formation method by the interface standby MBE method in the order of steps. here
A case where A _y B _1-y D ternary mixed crystal is laminated on the A _x C _1-x D ternary mixed crystal by the interface waiting MBE method will be described. In addition, A, B, and C are cationic, and D is an anionic element. Further, in the figure, the D element is omitted.

In Fig. 2, the molecular beam sources 20, 21, 22 and 23 are respectively
Put the raw materials of each element of A, C, B and D, open the shutters 5a, 5b and 5d in front of the molecular beam sources 20, 21 and 23 to open the A
After the growth of _x C _1-x D, a molecular beam source of A and C elements 20
The shutters 5a and 5b in front of and 21 are closed to irradiate only the D element. At the moment of interruption, as shown in FIG. 3 (a), there is unevenness having a height of two molecular layers on the surface. However, if the waiting period is continued for 90 to 180 seconds, A and C atoms or molecules on the surface diffuse on the surface and are captured by steps or kinks on the surface, as shown in FIG. 3 (b).
As shown in, a flat island having a height of one molecular layer is formed. Next, the shutters 5a and 5c in front of the molecular beam sources 20 and 22 of the A and B elements are opened, and A _y B is placed on the flattened surface.
By growing a _1-y D ternary mixed crystal, a desired hetero interface can be obtained as shown in FIG. 3 (c). The width of the transition region of the interface thus obtained is one molecular layer, which is extremely steep and flat.

[Problems to be Solved by the Invention] However, when the transition region of one molecular layer is examined in detail, this part is a quaternary mixed crystal in which A, B, and C elements coexist as cationic elements. Has become. This has the following disadvantages. That is, the quaternary mixed crystal is more likely to scatter carriers than the ternary mixed crystal. In addition, undesired disturbance of the energy potential occurs at the interface, which hinders the transport of carriers in the direction along the interface. This problem is because the quaternary mixed crystal composition in the transition region is not uniform in the plane parallel to the interface,
Especially important. The disturbance of the potential at the interface serves to expand the spectral width of exciton emission from the quantum well having such an interface. Therefore, it is a big problem when the quantum well is applied to an optical device.

The object of the present invention is to solve the above-mentioned conventional problems, and provides a method for forming a high-quality hetero interface by preventing the formation of an undesired mixed crystal at the interface. Especially.

[Means for Solving the Problems] The present invention is directed to a first semiconductor N-element mixed crystal (N represents a natural number of 3 or more) and a common cationic property with the first semiconductor N-element mixed crystal. In a method for forming a semiconductor hetero interface, a second semiconductor M-element mixed crystal (M represents a natural number of 3 or more) containing at least one element and at least one anionic element is laminated by a molecular beam epitaxy method. In the first growth step of epitaxially growing the semiconductor N-element mixed crystal, and by irradiating the molecular beam containing the cationic element and waiting while irradiating the molecular beam containing only the anionic element, A surface flattening step of flattening the surface of the first semiconductor N-ary mixed crystal grown in the first growth step so as to form a single molecular layer; and the first semiconductor N-ary mixed crystal and the second semiconductor M. Common cationic and anionic elements in mixed crystals A second growth step of growing a third semiconductor Q-source crystal or mixed crystal (Q represents a natural number of 2 ≦ Q ≦ N) consisting of one molecular layer, and the second semiconductor M-source mixed crystal as described above. And a third growth step of epitaxially growing on a third semiconductor Q-source crystal or mixed crystal.

[Operation] FIG. 1 is an explanatory view schematically explaining the method for forming a hetero interface according to the present invention in the order of steps. Here, a case of stacking an A _y B _1-y D ternary mixed crystal on an A _x C _1-x D ternary mixed crystal will be described. In addition, A, B, and C are cationic, and D is an anionic element.
Further, in the figure, the D element is omitted.

FIG. 1 (a) shows the surface of the underlying semiconductor ternary mixed crystal when the growth of the underlying A _x C _1-x D was stopped and the growth was stopped. Next, flattening is performed to obtain a surface state as shown in FIG. 1 (b), and then a crystal of an element common to the first and second semiconductor mixed crystals is grown for one molecular layer. As shown in FIG. 1 (c), only N-element mixed crystals are formed at the transition region of the interface. Then, as shown in FIG. 1D, a second semiconductor mixed crystal A _y B _1-y D is laminated to form a heterostructure. According to this method, unlike the conventional method, a mixed crystal having a higher order than that of the underlying mixed crystal, that is, a mixed crystal that easily scatters carriers is not formed, and an interface having high carrier transport efficiency can be obtained.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

As the MBE device used in the method of the present invention, for example, the device shown in FIG. 2 can be used. In the following, as an example, A in the explanatory diagram of FIG. 1 is In, B is Ga,
C is Al, D is As, and In _x Al _1-x As (x = 0.52) is used as the first semiconductor N-ary mixed crystal on the InP (001) substrate and the second M is used.
A case will be described in which In _y Ga _1-y As (y = 0.53) is stacked as a source semiconductor mixed crystal to form a heterostructure.

Each molecular beam source of the MBE device shown in Fig. 2 has 20
Ga is filled in n, 21 and Al in 22 and As in 23.

First, the InP (001) substrate 4 is organically cleaned by a usual method, chemically etched and then cleaned, and then 10 ^-10 Torr.
It is mounted on the substrate holder 3 in the growth chamber 1 which is evacuated to an ultrahigh vacuum of the table.

Prior to the start of growth, the In, Ga, and Al molecular beam sources 20, 21, and 22 have desired compositions, that is, In _x Al _1-x As (x = 0.52) and In _y Ga _1-y As.
The temperature is controlled so that (y = 0.53) is obtained. Also,
As molecular beam source 23 is also 2 × 10 ⁻⁵ Torr on the surface of InP substrate 4.
The temperature is controlled so that the strength of As molecular beam source 23
The shutter 5d in front of is opened, the temperature of the resistance heater attached to the substrate holder 3 is raised while irradiating the InP substrate 4 with the As molecular beam, and the surface of the InP substrate 4 is thermally cleaned under As pressure. Normally, the oxide film and dirt on the surface are removed at 540 ° C, and the surface becomes clean. Next, stabilize the substrate temperature at 550 ° C and
Open the shutters 5a, 5c in front of the Al and Al molecular beam sources 20, 22,
In _0.52 Al _0.48 As is grown to 0.5 μm (first growth step). The typical growth rate was 0.8 μm / h.

Next, the shutters 5a and 5c of the In and Al molecular beam sources 20 and 22 are closed to interrupt the growth. Here, the moment of interruption of growth is the first
It corresponds to FIG.

Next, while irradiating As as it is, the wafer is waited for 120 seconds to be planarized (planarization step). This state is the first
It corresponds to FIG.

Next, the shutter 5a in front of the In molecular beam source 20 is opened for 2.5 seconds corresponding to the thickness of one molecular layer, that is, about 2.93Å. The surface is covered with InAs by this second growth step (corresponding to FIG. 1 (c)).

Subsequently, the shutter 5b in front of the Ga molecular beam source 21 is opened, and In
_0.53 Ga _0.47 As is grown and a third growth step is performed.

Through the above steps, the hetero interface corresponding to FIG. 1 (d) is formed. At this hetero interface, there is no quaternary mixed crystal in the direction parallel to the interface, and the interface is a ternary mixed crystal.
is it abruptly switched from _{n x 'Al 1-x'} As to _{In y 'Ga 1-y'} As. Therefore, the conventional interface waiting MBE method cannot avoid it.
An interface transition region composed of a quaternary mixed crystal does not occur, and a high quality interface can be obtained. In _x ′ Al _1-x ′ As and In _y ′ G formed at the interface
Although a _1- y′As does not always have lattice matching with the InP substrate 4,
Since there is only one molecular layer, its effect can be almost ignored.

[Effects of the Invention] As described above, according to the method for forming a hetero interface of the present invention, the interface is formed from a flat island having a height of one molecular layer, is not only extremely steep, but also scatters carriers. In addition, an undesired mixed crystal layer that disturbs the energy potential is not generated. As a result, it is suitable for manufacturing an electronic device utilizing the carrier transport phenomenon along the hetero interface and for manufacturing an optical element using a quantum well in which mixed crystal (alloy) scattering at the interface affects the emission spectrum width.

[Brief description of drawings]

FIG. 1 is a process diagram schematically explaining the hetero interface forming method of the present invention, FIG. 2 is a schematic sectional view showing an example of an MBE apparatus used in the method of the present invention, and FIG. 3 is a conventional interface standby MBE.
FIG. 7 is a process diagram schematically illustrating a method for forming a hetero interface by the method. 1 ... Growth chamber, 3 ... Substrate holder 4 ... Substrate, 5a-5d ... Shutter 9 ... Vacuum pump, 20-23 ... Molecular beam source A, B, C ... Cationic element D ... Anionic element

Claims (1)

[Claims] 1. At least one cation element and an anionic element common to the first semiconductor N-element mixed crystal (N is a natural number of 3 or more) and common to the first semiconductor N-element mixed crystal. In a method for forming a semiconductor hetero interface, which comprises stacking second semiconductor M-ary mixed crystals (M is a natural number of 3 or more) containing each by a molecular beam epitaxy method, the first semiconductor N-ary mixed crystal is epitaxially grown. The first growth step and the irradiation of the molecular beam containing the cationic element are stopped, and the waiting is performed while irradiating the molecular beam containing only the anionic element.
A surface flattening step for flattening the step difference on the surface of the first semiconductor N-source mixed crystal grown in the growing step to form a monolayer.
A third compound composed of a cationic element and an anionic element common to the first semiconductor N-source mixed crystal and the second semiconductor M-source mixed crystal
A second growth step of growing only one molecular layer of the semiconductor Q elemental crystal or mixed crystal (Q represents a natural number of 2 ≦ Q ≦ N) of
A third growth step of epitaxially growing the second semiconductor M-element mixed crystal on the third semiconductor Q-element crystal or mixed crystal.